Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751506AbbDLKP7 (ORCPT ); Sun, 12 Apr 2015 06:15:59 -0400 Received: from mail-wg0-f46.google.com ([74.125.82.46]:35030 "EHLO mail-wg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751150AbbDLKP4 (ORCPT ); Sun, 12 Apr 2015 06:15:56 -0400 Date: Sun, 12 Apr 2015 12:15:51 +0200 From: Ingo Molnar To: Markus Trippelsdorf Cc: Linus Torvalds , Thomas Gleixner , Jakub Jelinek , Denys Vlasenko , Borislav Petkov , Tim Chen , Andy Lutomirski , Jason Low , Brian Gerst , Aswin Chandramouleeswaran , "Paul E. McKenney" , Davidlohr Bueso , Peter Zijlstra , "H. Peter Anvin" , LKML , Peter Zijlstra Subject: Re: [PATCH] x86: Turn off GCC branch probability heuristics Message-ID: <20150412101551.GB2862@gmail.com> References: <20150410092152.GA21332@gmail.com> <20150410111427.GA30477@gmail.com> <20150410112748.GB30477@gmail.com> <20150410120846.GA17101@gmail.com> <20150411092021.GA9478@gmail.com> <20150412054747.GA9062@gmail.com> <20150412062015.GA8458@x4> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150412062015.GA8458@x4> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1792 Lines: 45 * Markus Trippelsdorf wrote: > On 2015.04.12 at 07:47 +0200, Ingo Molnar wrote: > > > > * Linus Torvalds wrote: > > > > > On Sat, Apr 11, 2015 at 11:57 AM, Thomas Gleixner wrote: > > > > > > > > I thinks its just the no-guess one: > > > > > > > > text data dec patch reduction > > > > 7563475 1781048 10302987 > > > > 7192973 1780024 9931461 no-guess -4.8% > > > > 7354819 1781048 958464 align-1 -2.7% > > > > 7192973 1780024 9931461 no-guess + align-1 -4.8% > > > > > > Yeah, a 5% code expansion is a big deal. Sadly, it looks like > > > 'no-guess' also disables our explicit likely/unlikely handling. > > > > So I spent some time trying to get as much code size reduction as > > possible via GCC optimization options, and the total savings possible > > are 10.1%: > > > > text data bss dec filename > > 12566391 1617840 1089536 15273767 vmlinux.vanilla > > 11416805 1617840 1089536 14124181 vmlinux.combo > > 10532552 1596080 1089536 13218168 vmlinux.Os > > If you like to play with more knobs you could explore the various > --param options that are listed in the gcc man page... Well, I had a look, they are rather incomplete (at least as far as branch optimizations go), and I wouldn't want to rely on them for production kernel patches in any case, only on the more well-known compiler options. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/